For a very simple reason.
The PSP is different to other consoles in that there is very little correlation between userbase and software sales.
If the console is making $50 per unit (it could be a little less or a lot more) and you know having more out there won't effect software sales very much, why drop the price and lose hardware cash on a wasted venture?
starcraft - Playing Games = FUN, Talking about Games = SERIOUS







